The present invention relates to tubular prostheses, and, more particularly, to woven tubular prostheses having increased wall stiffness.
In the past, tubular prostheses have commonly been manufactured by, for example, weaving a plurality of warp yarns and a plurality of fill yarns into a tubular fabric. Such products, however, typically lack sufficient radial stiffness to maintain an open lumen, i.e., if unsupported, they will radially collapse. The tendency to radially collapse or kink is particularly problematic to a surgeon during implantation of the prosthesis.
Conventional weaves used for vascular grafts and other medical devices are known as simple weaves, i.e., one-ply weaves. These types of constructions are inherently strong with respect to burst pressure, but suffer from the above-mentioned kinking and collapsing tendencies, as well as the tendency to ravel at the ends, making it difficult to properly hold sutures. Additionally, the one-ply structure has inherent limitations as to the properties which can be engineered into the final woven product. For example, simple weaves do not stretch well radially or longitudinally and, further, possess only a simple pore structure due to the single layer.
To overcome these characteristics, prior art prostheses are typically crimped at equidistant lengths along their longitudinal axis. The crimping is believed to provide the prosthesis with sufficient radial stiffness to maintain an open lumen. The crimping additionally provides a degree of longitudinal compliance to the prosthesis.
Crimping, however, is not without its disadvantages. For example, the crimps create a plurality of irregularities along the inner wall of the prosthesis that may create blood flow disturbances. These blood flow disturbances become more pronounced and consequently less acceptable as the diameter of the prosthesis is reduced. In addition, thrombi can accumulate in the valleys of the crimps, tending to form hyperplastic pockets.
An alternative prior art technique for providing radial stiffness to a woven prosthesis involves the use of a stiffening component. Specifically, the fabric is woven around a suitable stiffener or, alternatively, such a stiffener is secured to either the interior or exterior of the prosthesis following weaving. The use of a stiffener, however, creates its own drawbacks. For example, tissue ingrowth may be hindered by the stiffener, the porosity of the prosthesis may be affected by the stiffener and, finally, the ability to suture the prosthesis to the host vessel may be hindered by the stiffener.
It would therefore be desirable to provide a woven tubular prosthesis that contains sufficient inherent wall stiffness so as to be radially self-supporting. Such a graft would not require crimping or the use of stiffening components, thereby providing a smooth, continuous inner wall that better simulates the natural hemodynamics of the connecting vessels, even with respect to those prostheses having a relatively small diameter, e.g., down to about 4 mm. Additionally, the same prosthesis would be less prone to pinching, kinking or other collapsing tendencies when subjected to bending forces, as well as being resistant to ravelling when cut to size during surgery. The prosthesis would also have the ability to hold sutures well. Finally, the pore structure would be more tortuous, thereby providing better hemostasis at the time of implantation and the ability to support long term healing and tissue incorporation.